Traditionally, tapes have been used as the primary storage medium for backup and archival data. To automate the mounting and dismounting of tapes into tape drives, many organizations use a robotically controlled tape library (or tape jukebox).
Actual usage of individual tape media is generally very small and infrequent. Backup jobs typically run at night during a period called the “backup window”. Most sites aim to limit the backup window to a small number of hours which is considered to be a short period of time.
Typical sites use tape rotation schemes whereby they write to daily tapes, weekly tapes and monthly tapes. Most tapes are sent off-site after being written to, and are not accessed again until either a restore is required (very infrequent) or the data on the tape has expired (usually after some number of weeks, months or even years). The result is that for most of the time, the majority of tapes are not accessed at all.
Instead of using a traditional tape drive or tape library, an organization can use a “virtual tape library”. A virtual tape library is similar to a physical tape library except that the data is stored on disk instead of tape. Existing virtual tape library solutions make use of a regular disk subsystem for storage.
Disk subsystems have completely different patterns to tape media. For example, disk subsystems in large organizations are accessed twenty-four (24) hours a day, seven (7) days a week. Most smaller organizations typically leave their fileservers powered on twenty-four (24) hours a day. Many applications (e.g. email and web services) need to be available twenty-four (24) hours a day for proper operation. Essentially, most disk subsystems are designed for frequent and sometimes continuous access.
When used with virtual tape library systems, disk subsystems suffer unnecessarily from the following problems: 1) they consume excessive amounts of power as all disks are left powered on at all times even though only a very small number are needed at any one time; 2) the long power on hours lead to failure caused by head movement, continuous disk spinning and thermal aging; and 3) the continuously energized disks are potentially at risk of being subjected to power surges which could harm or destroy the stored data.
As an example, disk drives in laptop computer systems consume a significant amount of power when in operation. For example, a two point five (2.5 in.) inch disk drive may consume up to thirty (30%) percent of total system power, while a one point eight (1.8 in.) inch drive may consume up to twenty (20%) percent. Accordingly, many laptop disk drives implement an electronic power down mode that is used to conserve battery power. However, this electronic power down mode fails to physically isolate the laptop disk drive such that the disk drive is protected against surges and viral attack.
Clearly what is needed is a protectable data storage system that physically isolates disks not being accessed by the system and thus eliminates damage from power surges and viral attacks; that provides improved disk reliability; that produces a reduced amount of thermal stress and produces less wear on the disk drive bearings; that allows an increased number of disks to be housed in a given volume of space; and that reduces energy costs due to improved operating efficiency.